Regulator

ABSTRACT

A regulator for regulating the electrical current supplied to an electrical apparatus by intermittently switching on and off said current. The regulator includes an electrically-heated expansion system acting on an electric switch for the apparatus. The invention calls for a pressure cell for bearing on the switch which is hydraulically connected to a hydraulic chamber remote from said pressure cell, an expansible liquid being contained in the hydraulic system and electric heating means being provided for treating the expansible liquid contained in the hydraulic chamber, such heating being dependent upon the magnitude of the current supplied to said electrical apparatus.

United States Patent [30] Foreign Application Priority Data Apr.'23, 1969 Germany ..P 19 20 550.6 Apr. 23, 1969 Germany ....P 19 20 552.8 Apr. 23, 1969 Germany ..P 19 20 5539 52 us. c1 ..331/319, 337/324 [5 1] Int. Cl. ..ll0lh 37/10, HOlh 37/20, H0lh 37/36 [58] Field oiSearch ..337/299,3l2,317,318,319, 337/321, 323, 324, 309, 31 l, 394, 310

[56] References Cited UNITED STATES PATENTS I 3,214,539 10/1965 Glaberson et al... .....337l3l1 2,215,384 9/1940 Wilkinson .337/394 X 3,342,976 9/1967 Kjellberg... .....337/324 X 2,878,580 3/1959 Hughes .337/324 X 3,274,362 9/1966 Fendock ..337/321 X Fischer f I [451 June 6, 1972 i 1 REGULATOR 2,853,583 9/1958 Rauh ,.337/323x [72] inventor: Karl Fischer, Oberderdingen, Am Gan- FOREIGN PATENTS OR APPLICATIONS sberg, Germany 1,134,136 8/1962 Germany ..337 309 [221 APP-20,1970 315,153 7/1956 Switzerland... ...337/321 21 APPLNQ; 29,3 5 655,989 8/1951 Great Britain ..337/324 Primary Examiner-Velodymyr Y. Mayewsky Assistant ExaminerDewitt M. Morgan Attorney-Brumbaugh, Graves, Donohue & Raymond [5 7] ABSTRACT A regulator for regulating the electrical current supplied to an 5 Claims, 7 Drawing Figures REGULATOR The invention relates to an energy regulator for electrical apparatus or equipment, particularly electrical heating equipment, which regulates by intermittently switching on and off and which incorporates an electrically heated expansion system acting on an electrical switch, particularly on a snap switch. Such a regulator will be referred to hereafter as a regulator of the type described.

Energy regulators of this type have become known, for example, as regulators for electric hot plates.v They possess an electrically heated bimetal strip which acts on the pressure point of a snap switch and through which the heating current passes. Alternatively the heating current may pass through a parallel'circuit to the bimetal strip. The heating current is switched on and off by the snap switch. The position of the bimetal strip in relation to the snap switch can be altered by means of a control linkage, to enable difierent outputs to be set. When the hot plate is switched on, the bimetal strip is heated. It then acts on the snap switch in the switch-off direction; When the hot plate is switched off the bimetal strip cools down and accordingly switches the heating current on again. In thisway an intermittent control is obtained.

Regulators operating with heated bimetal strips have the advantage that the bimetal strip produces relatively long regulating strokes, so that their motion requires very little transmission in order to actuate the switch. On the other hand however the bimetal strip only produces very low forces which do not ensure reliable switching. The conventional snap switches generally used in these regulators have an actuating force of approximately 400 grams. If a force of this order is to be obtained with a bimetal strip, the latter must either by exceptionally large or it must be prestressed to a very high extent until the switching force has been overcomefilhis however results in inaccuracies, so that accurate switching is no longer ensured. A bimetal strip has the further disadvantage that it becomes unstable at high temperatures, i.e., its deflection force and deflection stroke are no longer linear. Accordingly a system of this type usually needs to be compensated in order to obtain repeatable conditions. The thermal compensation which is intended to eliminate interference from the ambient temperature,'displays the samedefects. This shows that it is exceptionally difficult to obtain repeatable conditions with conventional regulators. c

It has already been suggested that a heated metallic expansion sleeve be used in place of the bimetal strip. This has the advantage that virtually unlimitedforces can be transmitted and the linearity is improved. There is however the disadvantagethat the components linking the two ends of the expansion sleeve are likewise influenced by the ambient temperature, which renders additional compensation necessary.

An expansion sleeve with an internal Invar rod, in which the two reference points are close together, produces somewhat better results. In this case too, however, complete linearity is not obtained, since the lnvar rod reaches very high temperatures in the sleeve and does not therefore have completely linear characteristics. Moreover, expansion sleeves have very low expansion values. under the prevailing spatial conditions. With standard sizes and temperatures, these values are about one-tenth mm between the heated and unheated condition. For improved setting, the expansion of the sleeve opposite the snap switch must therefore be passed through a linkage system which entails the use of lever mechanisms which make the regulator more elaborate and add further inaccuracies to the system. If it were desired to allow the relatively low expansion to act directly on the switch, a very elaborate setting mechanism would be required for the regulator, a conventional screw spindle no longer being sufficient. Precision cams for adjusting the switch or the lever mechanism would be required.

The principle object of the present invention is to supply a regulator of the type described, which avoids the above mentioned disadvantages. The regulator is intended to eliminate the need for elaborate lever mechanisms and enable an easily produced control linkage to be used, at the same time providing accurate compensation inthe simplest manner.

This object is achieved according to the invention by incorporating in a regulator of the type described a hydraulic system with a pressure cell acting on the switch and a chamber which is connected with the pressure cell, the hydraulic system being filled with expansible liquid and electrically heated in accordance with the current supplied to the electrical apparatus.

This arrangement avoids all the disadvantages of the proposed or conventional systems. The expansion strokes available at the pressure cell can be set as desired to the most advantageous value by changing the size of the pressure cell or chamber. The available force is considerably greater than in the bimetal strip constructions, and the expansion system has linear characteristics. Moreover, heating need not be very intense, hence the influences exercised on the environment are diminished. The link between the chamber and the pressure cell is a capillary tube. This also permits a large measure of independence in the layout; the chamber can be located in the most favorable position from spatial, electrical and heat engineering considerations.

According to a particularly advantageous embodiment of the invention, the pressure cell is directly interposed by mechanical means between a control linkage, preferably manually operated, and the pressure point of the switch. It should be noted that no lever mechanism of any kind is required; the individual components of the regulator being arranged in a positive relation directly behind one another. It is particularly advantageous to include a thermal compensation device in the control linkage of the energy regulator. This device preferably consists of a sleeve made from material having a high thermal expansion coefficient axially retained at the end facing the switch and a rod made from material with a low thermal expansion coefficient located in the sleeve and axially fixed on the sleeve on the other side.

According to a further feature of the invention, the rod is axially fixed in the sleeve by means of an adjusting screw, enabling easy adjustment of the regulator from the outside of the switch. 7

According to a further embodiment of the invention, the electrically heated chamber consists of a metal sleeve having a connection tube to the pressure cell, and incorporates an electrical resistance heating. The heating device may be in the form of a sheet metal casing through which current passes or consist of a wire coil. It is particularly advantageous if the walls of the electrically heated chamber form the heating resistance. Hence the chamber can be designed in a particularly simple way. This embodiment of the invention is possible largely because of the fact that the chamber may be made of electrical resistance material in place of the material with a high thermal expansion coeflicient required for the expansion elements. Since the regulator is a completely self-contained unit, it is not absolutely essential to electrically insulate the pressure cell from the chamber. No harm is caused if the latter is conducting current. In this case, however, it is an advantage if, according to further features of the invention, the pressure cell is electrically insulated from the control linkage and possibly from the switch.

In the upper output range it is unnecessary, particularly with electrical heating apparatus, to make fine graduations of output. The known types of regulator are not very accurate in this upper output range. Raising the temperature at the expansion element in this range causes only a slight change in length so that the regulators are usually set so that they are infinitely variable only up to about percent, whereupon the full power of the apparatus is switched on. Here, however, the expansion elements, which are then continually heated, reach very high temperatures and thus influence the overall temperature of the regulator too. The insulation of all components, particularly those for the heating of the expansion elements, must therefore be designed for continuous high temperatures. The operating temperature of the expansion element must be set correspondingly lower, since a safety margin must be left for the continuous load. In order to eliminate these disadvantages, according to a further feature of the invention, an auxiliary contact is provided which cuts out the electrical heating for the chamber at the highest output to which the regulator can be set. More particularly in electrical heating apparatus which are often operated for lengthy periods at full capacity, such as electrical hot plates when heatingwater, this valuable feature makes it possible to adjust the output in the lower range (continued boiling in the case of electrical hot plates) with particular precision and reliability.

The invention makes it possible to design the control linkage as a simple screw spindle. On account of the linearity of the expansion of the hydraulic system, the output gradation can likewise be marked linearly in the control, which is usually amanually rotatable knob. This makes it easy and convenient to operate the regulator.

Further'advantages and features are detailed in the specifications and claims. The invention will now be further described further by way of example with reference to the accompanying drawings, in which:

FIG. 1 is a diagrammatic representation of a regulator according to the invention;

FIGS. 2 to 4 show a circuit of a regulator according to the invention in three different output stages;

FIG. 5 shows an alternative embodiment of the invention;

FIG. 6 is a diagrammatic illustration partly in section of an alternative compensation device; and

FIG. 7 is a longitudinal illustration partly in section of a regulator according toan alternative embodiment of the invention. I

The regulator of FIG. 1 includes an electrical switch 11 which is designed'as a snap switch consisting essentially of a snap spring 12 supporting a movable contact 13 which operates in conjunction with a fixed contact 14. The current for an electrical apparatus or equipment, e.g., an electric hot plate, is controlled via the contacts 13, 14. The switch 11 is attached to a housing in the regulator which is not illustrated. A pressure cell 16 acts on a pressure point 17 of the switch 11 via an insulated rocker arm 15, which consists of a rotatably mounted lever having an insulated knob attached thereto at one end. The pressure cell 16 is in the formbf a metallic 'diaphragm cell which is connected by a metal capillary tube 18 to a chamber 19.

The pressure cell 16, capillary tube 18 and chamber 19 form an expansion system which is filled with an expansible liquid. The chamber 19 is electrically heated. This can be done for example by fitting an electrical resistance heating element round the chamber. This element can consist of a wire coil or a casing made of electrical resistance material. It is however particularly advantageous if the walls of the chamber themselves form the heating resistance. In this case the chamber can for example be made of a small tube of electrical resistance material; Electrical current is supplied to this tube via a pair of connections 20, 21 located at both ends thereof.

Upon energization of the chamber 19 the pressure cell is likewise energized, since the capillary tube 18 is made of metal. The pressure cell 16, is, however, electrically insulated by the insulated rocker arm from switch 1 l and by a further insulation against the other parts of the switch. A control linkage 22, designed as a screw spindle, bears on the pressure cell 16. The control linkage 22 consists of a sleeve 23 made of a material having a high thermal expansion coefficient, such as brass, and a rod 24 fitted therein made of a material having a low thermal expansion coefficient, such as Inuar. The sleeve 23 is externally threaded and cooperates with a nut 25 on its end facing the pressure cell 16. At its opposite end the sleeve 23 is connected to the rod 24 by an adjusting screw 26. The rod 24 acts on the pressure cell directly or via an electrical insulating device, but without any transmission linkage. Three electrical switch contacts 27, 28, 29 are actuated by cam (not illustrated) on the screw spindle 22.

FIGS. '2 to 4 show the regulator of FIG. 1 regulating the current flow to an electrical apparatus 30. The latter is supplied from two electrical supply lines 31, 32. The switch contacts 27, 28 form 'a double-pole isolating switch which in the switched-off condition electrically separates the electrical apparatus 30 from the supply lines 31, 32. Current is supplied to the electrical apparatus 30 via the contact 13, 14 and the heating circuit of chamber 19. The switch contact 29, which forms an auxiliary contact described in greater detail below, is connected in parallel with the heating element of chamber 19. The regulator illustrated in FIGS. 1 to 4 operates in the following manner:

In the switched-off condition shown in FIG. 2 the contacts 13, 14, 27, 28, 29 are all open, and the electrical apparatus 30 is thus deenergized. In this position the screw spindle is rotated by a manually operated control knob 33 (FIG. 1) so that the pressure exerted by the spindle on pressure point 17 of the switch 11 (via the pressure cell 16 and the insulating rocker 15) keeps the switch 11 in the open position. The screw spindle 22 is screwed furthest into the nut 25 in this position. The cams on the screw spindle 22 keep the contacts 27, 28, 29 open.

When the apparatus is switched on by turning the spindle by means of the control knob 33 (see FIG. 3) the two switch con tacts 27, 28 of the double-pole isolating switch are closed. At the same time the screw spindle is screwed out of the nut 25 until the pressure cell 16 yields slightly in an axial direction and actuates the switch 11 as a result of the action of the snap spring 12, so that the current flows from the feed lines 31, 32 via the heating element of chamber 19 and the electrical apparatus 30. Heating of chamber 19 causes the expansible liquid inside it to expand so that the diaphragm of the pressure cell 16 is deflected and, since the pressure cell is supported against the screw spindle, exerts increased pressure on the pressure point 17 of the switch. The switch 1 l is therefore cut out again after an interval which corresponds to the setting of the regulator the contacts 13, 14 are separated. As a result, both the electrical heating apparatus and the chamber 19 are separated from the supply line. In consequence, the chamber 19 and the expansible liquid cool down, so that the pressure cell 16 contracts again and switch 1 l is actuated once more. It can be seen that in this way intermittent switching on and off of the current for the electrical apparatus 30 takes place which switching is dependent on the setting of the regulator, i.e., the setting of the screw spindle 22. The auxiliary contact 29 is open in the usual adjustment range of the energy regulator, which normally covers 7 to 65 percent of the full output.

With full output (FIG. 4), which is switched on by a further turn of the screw spindle 22, the auxiliary contact 29 is closed. The latter bridges the heating element of the chamber 19, so that the chamber 19 remains cold even when the electrical apparatus 30 is energized. This arrangement, made according to a feature of the invention, offers the following advantages. The fact that when the auxiliary contact 29 is closed the chamber 19 is no longer heated and the pressure cell 16 consequently remains continuously in its contracted state ensures that the full output is always available, i.e., quantizing is interrupted. Otherwise, if the setting of the regulator is not completely accurate, the expansion element constantly continuing to be heated is liable to cause further quantizing, i.e., a decrease in output, despite a setting of the regulator spindle which is intended to correspond to the full output. This can only be avoided by providing a relatively high angular range for the full output on the regulator spindle. Moreover, the expansion element which in the present case consists of the pressure cell 16, the capillary tube 18 and the chamber 19, would be raised to high temperatures, because of the uninterrupted heating, and impose unnecessary thermal strains on the entire regulator. The compensation device described hereafter would have to be designed for higher temperatures and the expansion liquid would need to be more temperature-resistant or the design of the entire quantizing system would need to be based on a lower temperature level. All these disadvantages are avoided. If the auxiliary contact 29 is cut in, for which a comparatively low angular range of the regulator spindle is sufficient, no further quantizing occurs, and the switch 11 is firmly held in the closed position. The entire regulator and especially the expansion system is not heated unnecessarily when for example water is to be brought to the boil on an electric hot plate at full output. The electrically heated expansion system need not be designed for full output, hence the temperature difference suitable for quantizing may be raised if there is a risk of maximum temperature caused by possible impairment of the expansible liquid, which can rise to over 300 C.

FIG. 5 shows an alternative circuit to that illustrated in FIGS. 2 to 4 which is in a switched-off condition. In this case the chamber 19 is connected in parallel to the electrical heating apparatus 30 and not, as in FIGS. 1 to 4, permeated by the entire current supplied to the electrical apparatus 30. The auxiliary contact 29' is normally closed in this case, and is switched off at full output.

The regulator is liable to reach very high temperatures as a result of either environmental influences or of the heat generated by the heated expansion system. These temperatures exceed those created by the heating of the chamber 19, hence if the ambient temperatures vary there would be a change in the output produced with a specific spindle setting. To counteract this a thermal compensation device is provided which is built into the control linkage 22 as shown in FIG. 1. If the temperature is raised the sleeve 23 expands considerably more than the rod 24, so that the rod 24 is recessed within the sleeve 23 with the same spindle setting in relation to the nut 25. The compensation device is set in such a manner that this recessing of the rod 24 corresponds to the expansion of the pressure cell 16 caused by the ambient temperature. The fact that the hydraulic expansion system l6, 18, 19 operates over the entire temperature range in question almost completely linearly is a considerable advantage of the invention. In this way the compensation device can likewise operate with a linear characteristic, and repeatable conditions are always obtained.

The alternative compensation device shown in FIG. 6 consists of a bimetal strip 34 interposed between the pressure cell 16 and the pressure point 17 of the switch. The bimetal strip 34'may be fixed on the insulated rocker arm 15. The compensating device shown in FIG. 1 has however the advantage of having complete linearity. In combination with the hydraulic system particularly favorable conditions may be obtained. Any desired expansion can be obtained by selection of the chamber size 19, the size of the pressure cell 16 and the expansible liquid, with a pre-set temperature difference (in practice approximately 200 C) effective for quantizing. It has been found that a useful stroke of thirty one-hundredths to forty one-hundredths mm of the pressure cell can be obtained with an advantageously low total volume and a design of the pressure cell which is advantageous from the point of view of manufacture. This stroke represents an optimum when using a conventional snap switch having a stroke of one one-hundredth to two one-hundredths mm. The resulting ratio of l 30 to l l5 enables reliable pre-selection of the desired control points.

Temperature differences from 100 to 140 C in the ambient temperature are liable to arise in a regulator. In the expansion system described this would correspond to a stroke of approximately ten one-hundredths mm, which would need to be compensated. This stroke can easily be obtained with the compensation device illustrated in FIG. 1 in the case of a standard size regulator. This means that it is possible to advantageously arrange the compensation device, pressure cell and switch directly behind one another, without any elaborate and trouble-prone transmission mechanism.

The chamber 19 can be designed simply and can consist of a thin tube closed at the front and rear by deformation, the capillary tube being inserted in one end. The heat emission of the chamber 19 is adjustable over a very wide range dependent on its diameter, configuration and location. Since the heated element is connected with the pressure cell via a tube, it may be fixed in or on the regulator in a place where its influence on the temperature in the regulator becomes extremely slight. It is therefore desirable to locate the chamber 19 outside the actual regulator, for example in a separate housing or in a part of the housing separated from the mechanical part of the regulator by heat insulation.

The fact that the chamber 19 can be used directly as heating element must also be regarded as an exceptional advantage of the regulator according to the invention. The insulation between the expansion element and its heating element formerly customary and necessary, can now be completely dispensed with, which means that optimum conditions for heat transmission are obtained.

The length of the effective expansion stroke of preferably thirty one-hundredths to forty one-hundredths mm which can be obtained with the system according to the invention also makes it possible to design the control linkage as a simple screw spindle. It was usually necessary to interpose a transmission system in the conventional regulators, since for practical use it is impossible to make a screw spindle the pitch of which is below a certain value. For this reason a cam was frequently used, which is extremely difficult to manufacture. The invention makes it possible to use a spindle pitch of, e.g., 0.5 mm, which is still easy to make. The range of stepless adjustment from approximately 7 to 70 percent of the total output can then extend over approximately two-thirds of a complete spindle revolution, so that the favorable range between thirty onehundredths and forty one-hundredths mm for the useful stroke is again achieved.

FIG. 6 shows an alternative to the regulator of FIGS. 1 to 4 without contacts 27, 28, 29. This enables the control knob 33 to be directly connected to the nut 25 of the screw spindle 22. In this way the height of the regulator may be kept very low, a contributory factor being the flat design of the compensation device with the bimetal strip 34. The double-pole isolating switch 27, 28 can be replaced by a separate switch, for example a simple pushbutton. This results in a low height regulator of simple design.

Furthermore, FIG. 6 shows that a temperature probe 40 filled with expansible liquid can be connected to the pressure cell 16 in addition to the heated chamber 19. The temperature probe 40 can be capable of being pressed on the bottom of a pot 42 standing on an electrical hot plate 41 in known manner. A separate pressure cell which acts on the switch 11 in the same manner as the pressure cell 16 can also be provided for the temperature probe.

The embodiment of FIG. 7 is particularly easy to manufacture. It comprises the same essential components as those represented in diagrammatic form in FIG. 1. Identical components bear identical reference numbers. The parts of the regulator such as nut 25, switch contacts 27, 28, 29, which are actuated by cams 50 on the screw spindle 22, switch 11, are arranged on a baseplate 45 which in the main extends parallel to the control linkage. The latter may contain the described compensation device, i.e., the rod 22. The baseplate has attachments 58 on the outside in the form of flat plugs angled in the direction of the regulator inside, which allow the connecting cables which are provided with suitable connections to be simply pushed on. The control linkage is guided via a sleeve 63, which is connected to the baseplate by means of an angled stirrup 61. The switch 11 is likewise attached to the baseplate by an L-shaped stirrup 62. It can be seen that this arrangement considerably simplifies the assembly of the switch and the leading out of the electrical connections. The latter need only be conducted through apertures in the baseplate which also serve to fix the contacts. It will be apparent that in this case too the height of the regulator can be reduced by placing one of the switch contacts, e.g,, the signal contact, on the opposite side of the control linkage.

The invention permits numerous variations of the embodiments illustrated in the drawing. For example, the heating current could be transmitted to the chamber direct via the snap spring, the pressure cell and the capillary tube.

I claim:

1. A regulator for regulating the electrical current supplied to an electrical apparatus such as a hot plate by intermittently switching on and off said current, which regulator includes an electrically heated expansion system acting on a pressure point of an electric switch for said apparatus, wherein the improvement comprises a pressure cell bearing on the pressure point of said switch; a hydraulic chamber remote from said pressure cell; hydraulic circuit means connecting said pressure cell and said hydraulic chamber, said pressure cell, hydraulic chamber and circuitmeans together defining a hydraulic system; an expansible liquid contained in said hydraulic system; electric heating means for heating said expansible liquid contained in said hydraulic chamber, such heating being dependent upon the magnitude of the current supplied to said electrical apparatus; a manually operated control linkage comprising a screw spindle having a screw sleeve which, when turned, provides an axial control movement for the regulator; and mechanical means for supporting said pressure cell between said control linkage and the pressure point on said ;witch; wherein a thermal compensation device is built into said control linkage, said thermal compensation device being formed of said sleeve which is made from a material having a high thermal expansion coefficient, said sleeve being retained axially at an end facing the switch, and a rod made from a material having a low thermal expansion coefficient located in said sleeve and axially retained in said sleeve at the opposite end of said sleeve by fastening means acting in at least one axial direction, said rod bearing on said pressure cell.

2. Regulator as set forth in claim 1, wherein said fastening means comprises an adjusting screw screwed into said sleeve and bearing on said rod.

3. A regulator for regulating the electrical current supplied to an electrical apparatus such as a hot plate by intermittently switching on and off said current which regulator includes an electrically-heated expansion system acting on an electric switch for said apparatus wherein the improvement comprises a pressure cell bearing on said switch, a hydraulic chamber remote from said pressure cell, hydraulic circuit means connecting said pressure cell and said hydraulic chamber, said pressure cell, hydraulic reservoir and circuit means together defining a hydraulic system, an expansible liquid contained in said hydraulic system, a control linkage controlling the location of said pressure cell with respect to said switch, said control linkage including a baseplate, a rotatable screw-threaded spindle arranged substantially parallel to said baseplate, a threaded nut cooperating with said spindle for adjustably positioning said spindle with respect to said cell, a plurality of switch contacts arranged in line on one side of said baseplate, and a plurality of cams mounted on said spindle and arranged to cooperate with respective one of said contacts, connection contacts for said regulator located on the opposite side of said baseplate, and electric heating means heating said expansible liquid contained in said hydraulic chamber, such heating being dependent upon the magnitude of the current supplied to said electrical apparatus.

4. Regulator as set forth in claim 3 wherein said connection contacts for said regulator are designed as flat plugs which are angled along at least part of their length with respect to the baseplate of said regulator.

5. A regulator for regulating the electrical current supplied to an electrical apparatus such as a hot plate by intermittently switching on and off said current, which regulator includes an electrically heated expansion system acting on an electric switch for said apparatus, wherein the improvement comprises a pressure cell bearing on said switch; a hydraulic chamber remote from said pressure cell; hydraulic circuit means connecting said pressure cell and said hydraulic chamber, said pressure cell, hydraulic chamber and circuit means together defining a hydraulic system; an expansible liquid contained in said hydraulic system; electric heating means for heating said expansible liquid contained in said hydraulic chamber, such heating being dependent upon the magnitude of the current supplied to said electrical apparatus' an auxiliary electrical contact; a control linkage for controlling the location of said 

1. A regulator for regulating the electrical current supplied to an electrical apparatus such as a hot plate by intermittently switching on and off said current, which regulator includes an electrically heated expansion system acting on a pressure point of an electric switch for said apparatus, wherein the improvement comprises a pressure cell bearing on the pressure point of said switch; a hydraulic chamber remote from said pressure cell; hydraulic circuit means connecting said pressure cell and said hydraulic chamber, said pressure cell, hydraulic chamber and circuit means together defining a hydraulic system; an expansible liquid containEd in said hydraulic system; electric heating means for heating said expansible liquid contained in said hydraulic chamber, such heating being dependent upon the magnitude of the current supplied to said electrical apparatus; a manually operated control linkage comprising a screw spindle having a screw sleeve which, when turned, provides an axial control movement for the regulator; and mechanical means for supporting said pressure cell between said control linkage and the pressure point on said switch; wherein a thermal compensation device is built into said control linkage, said thermal compensation device being formed of said sleeve which is made from a material having a high thermal expansion coefficient, said sleeve being retained axially at an end facing the switch, and a rod made from a material having a low thermal expansion coefficient located in said sleeve and axially retained in said sleeve at the opposite end of said sleeve by fastening means acting in at least one axial direction, said rod bearing on said pressure cell.
 2. Regulator as set forth in claim 1, wherein said fastening means comprises an adjusting screw screwed into said sleeve and bearing on said rod.
 3. A regulator for regulating the electrical current supplied to an electrical apparatus such as a hot plate by intermittently switching on and off said current which regulator includes an electrically-heated expansion system acting on an electric switch for said apparatus wherein the improvement comprises a pressure cell bearing on said switch, a hydraulic chamber remote from said pressure cell, hydraulic circuit means connecting said pressure cell and said hydraulic chamber, said pressure cell, hydraulic reservoir and circuit means together defining a hydraulic system, an expansible liquid contained in said hydraulic system, a control linkage controlling the location of said pressure cell with respect to said switch, said control linkage including a baseplate, a rotatable screw-threaded spindle arranged substantially parallel to said baseplate, a threaded nut cooperating with said spindle for adjustably positioning said spindle with respect to said cell, a plurality of switch contacts arranged in line on one side of said baseplate, and a plurality of cams mounted on said spindle and arranged to cooperate with respective one of said contacts, connection contacts for said regulator located on the opposite side of said baseplate, and electric heating means heating said expansible liquid contained in said hydraulic chamber, such heating being dependent upon the magnitude of the current supplied to said electrical apparatus.
 4. Regulator as set forth in claim 3 wherein said connection contacts for said regulator are designed as flat plugs which are angled along at least part of their length with respect to the baseplate of said regulator.
 5. A regulator for regulating the electrical current supplied to an electrical apparatus such as a hot plate by intermittently switching on and off said current, which regulator includes an electrically heated expansion system acting on an electric switch for said apparatus, wherein the improvement comprises a pressure cell bearing on said switch; a hydraulic chamber remote from said pressure cell; hydraulic circuit means connecting said pressure cell and said hydraulic chamber, said pressure cell, hydraulic chamber and circuit means together defining a hydraulic system; an expansible liquid contained in said hydraulic system; electric heating means for heating said expansible liquid contained in said hydraulic chamber, such heating being dependent upon the magnitude of the current supplied to said electrical apparatus; an auxiliary electrical contact; a control linkage for controlling the location of said pressure cell with respect to said switch, said control linkage including means for operating said auxiliary contact when said control linkage is set in the upper output range of the regulator, said auxiliary contact being electrically connected with the linE supplying electrical power to said electric heating means of said chamber and constituting means for switching off the electrical power thereto upon operation, thereby switching off the electrical heating for said chamber when the regulator is in the upper output range. 